Pellets of ceramic materials are desired in many applications. Depending on the ceramic constituents, the pellets can exhibit different properties. For example, a suitable ceramic material having catalytic properties could be selected and formed into pellets having catalytic properties, or a ceramic carrier material could be selected for the preparation of pellets of catalyst carrier material. There are a number of conventional methods that can be used for preparing ceramic pellets, such as different moulding methods, optionally in combination with conventional powder processing methods used for manufacture of ceramic or metallic components.
The forming of spherical pellets requires sophisticated moulds in order for the pellets to be spherical and exhibit a smooth surface. The mould will for example generally have a exhibit a certain draft angle, which will cause imperfection in the surface of the pellet. Demoulding of the pellet will rarely be perfect and fractions of the moulded material are prone to stick to the mould, which will then be separated from the pellet during demoulding. These problems generally become more pronounced as the desired diameter of the pellet to be moulded decreases. JP8059352 describes a method for granulating a ceramic material with no need for a large-scale equipment and without causing contamination, which also improves the degree of freedom in the production process. According to the method a slurry containing ceramic raw material is dropped on a smooth surface having a high water repellent property, and the dropped material can thereafter be rolled on the surface into a spherical shape. The drops are formed by the action of surface tension.
It is an object of the present invention to provide a simplified method of forming smaller sized, spherical pellets of a controllable, uniform size from a ceramic slurry.
For the general method according to which spherical pellets are prepared from a slurry comprising a ceramic powder, a solvent, and any desired additives by means of a drop-generating orifice to which said slurry is fed, this object has been achieved by which drops are released from the drop-generating orifice by means of a relative flow of a liquid medium in relation to the orifice, formed into spherical bodies in said liquid medium by the action of surface tension, and thereafter treated for consolidation.